The Post Office in Borough High Street was closed on Wednesday and Thursday after "unexpected issues" with building work in the branch.
"London Bridge Post Office has been undergoing refurbishment out of hours recently," said a Post Office spokesman.
"Unfortunately, unforeseen issues with the building work have arisen and we were unable to open the branch on Wednesday and Thursday. The branch will remain closed until further notice.
"We would like to apologise for any inconvenience this is causing customers. Post Office services are very important for people in the area, and we hope they will be able to use other Post Office branches in the area, including Blackfriars Post Office and City of London Post Office."